On Fri, Mar 31, 2017 at 01:02:51PM +0200, Andrzej Hajda wrote: > In this version of the patch I have replaced temporal pages and > iommu_dma_mmap with remap_pfn_range or rather its simplified version > vm_iomap_memory. > Unfortunately I have not find nice helper for sgtable creation, so I > left sg allocation inside _iommu_mmap_attrs. > > As the fixing of DMA_ATTR_FORCE_CONTIGUOUS related crashes has higher > priority I have focused only on it in this patch.
As I mentioned elsewhere, I don't believe that fudging around in this way is a proper fix. DMA coherent memory was never, ever, intended to be passed back into the streaming APIs - it was designed that the two would be mutually exclusive. The problem is that we now have DMA coherent allocations being passed through the dma-buf API using this dma_get_sgtable() thing, which is quite broken. I regard dma_get_sgtable() as very broken, and had I realised at the time that this was what it was trying to do, I would have NAK'd it. Rather than bodging around this brokenness, trying to get dma_get_sgtable() to work, I believe we need to address the root cause - which is proper support for passing DMA coherent allocations through dma-buf, which does not involve scatterlists and calling dma_map_sg() on it. That's going to need to be addressed in any case, because of the dma_declare_coherent_memory() issue, where we may not have struct pages backing a coherent allocation. Such a case can come up on ARM64 via DT's "shared-dma-pool" reserved memory stuff. Right now, I have a "fix" for ARM queued which causes dma_get_sgtable() to fail when used with reserved memory, but we have one user who needs this to work. So, dma-buf needs to be fixed for this one way or another, and I don't think that bending the current broken stuff to suit it by trying these vmalloc_to_page() hacks is acceptable. dma_get_sgtable() is fundamentally broken IMHO. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu